海水板式换热器微生物污垢特性的实验研究

海洋生物附着及低速海流等因素直接影响海水换热器换热效果。为研究海水板式换热器的污垢特性,本文采用自行设计的板式换热器实验装置,通过富集培养并分离出硫酸盐还原菌（SRB）,使其附着海水板式换热器设备,并利用扫描电镜及热阻试验台,实验研究了附着污垢层的形成、生长及其换热特性,并对低流速海流环境下换热器的污垢热阻特性进行了对比实验。实验结果表明：污垢层的形成在不同时期其形貌和特征不同。能谱分析显示其组成的元素主要为C、H、O、Ca,是由各种有机物和悬浮颗粒组成。在诱导期后,污垢热阻符合渐进污垢增长模型,1 m/s以内的低流速下污垢热阻随流速增大而增大。     

复合改性表面抑制颗粒污垢积聚特性分析

换热设备颗粒污垢一般指悬浮在流体中的固体颗粒在换热面上的积聚。开发了一种Ni-P-TiO₂防垢型复合改性表面,并将之用于板式换热器抑制纳米MgO颗粒污垢在换热表面的积聚。基于搭建的板式换热器颗粒污垢热阻动态监测实验系统,研究了不同冷却水流速(0.1~0.3 m/s)、入口温度(30~40℃)及纳米MgO浓度(100~400 mg/L)对Ni-P-TiO₂复合改性换热表面抑垢特性的影响。结果表明,随着流速的增加,污垢热阻渐近值减小了27.85%~34.41%;随着冷却水入口温度的升高,污垢热阻渐近值减小了25.15%~39.14%;随着MgO颗粒浓度的增加,热阻渐近值减小了26.15%~45.36%。结合Ni-P-TiO₂复合改性表面的表面能分析了其表面的抑垢性能,发现制备的Ni-P-TiO₂复合改性表面的表面能与纳米MgO颗粒污垢层的表面能相接近,符合Zhao提出的“最优表面能”抑垢理论。与常规板式换热器不锈钢表面相比,Ni-P-TiO₂复合改性表面不仅抑制了颗粒污垢的积聚,还降低了颗粒污垢的固着强度,使得积聚其上的颗粒污垢更容易被剥离换热表面,实现了换热表面持久高效抑垢。     

板式换热器铁细菌生物污垢特性的实验分析

为探讨铁细菌在板式换热器里的污垢规律,对不同流速、温度及浓度下铁细菌在板式换热器内的污垢特性进行了实验研究。结果表明：随着流速的增加,铁细菌的污垢热阻渐近值逐渐减小;随着温度的升高,铁细菌的结垢诱导期明显缩短,结垢速率加快,污垢热阻的渐近值呈减小的趋势;而随着浓度的增加,污垢热阻值呈现明显的增长。     

板式换热器铁细菌生物污垢特性的实验分析

为探讨铁细菌在板式换热器里的污垢规律,对不同流速、温度及浓度下铁细菌在板式换热器内的污垢特性进行了实验研究。结果表明:随着流速的增加,铁细菌的污垢热阻渐近值逐渐减小;随着温度的升高,铁细菌的结垢诱导期明显缩短,结垢速率加快,污垢热阻的渐近值呈减小的趋势;而随着浓度的增加,污垢热阻值呈现明显的增长。     

Ca2+环境下水质参数变化对板式换热器铁细菌微生物污垢的影响

换热设备微生物污垢形成机制和影响因素复杂,污垢数据和规律的获取难度较大。本文采用搭建的板式换热器循环冷却水实验系统,获得了加入Ca²⁺后板式换热器冷却水铁细菌微生物污垢热阻数据,研究了加入Ca²⁺后不同运行工况下冷却水水质参数（OD、pH、电导率）的变化,进一步分析了水质参数变化对微生物污垢生长带来的影响。结果表明,加入Ca²⁺后微生物污垢热阻渐变化明显。随着低温循环冷水进口温度增加,含有Ca²⁺和铁细菌的循环冷却水OD逐渐降低,pH则逐渐升高,电导率减小,微生物污垢热阻逐渐降低;随着流体速度的增加,循环冷却水OD则升高,pH降低,电导率增大,但流速的增大同样加剧了冷却水对通道壁面的剥蚀作用,导致微生物污垢热阻随流速增逐渐下降。     

板式换热器冷却水污垢热阻预测的偏最小二乘回归法

搭建板式换热器冷却水污垢热阻实验台,测得不同时间、流速和温度下天然循环冷却水（松花江水）中铁离子、氯离子、细菌总数、pH值、溶解氧、浊度、电导率等水质参数,随机取一组实验的水质参数作为输入变量,建立换热器冷却水污垢热阻预测的偏最小二乘回归模型,对板式换热器的污垢热阻进行预测。整个实验过程中,热水进口温度为43.5～44.5℃,冷却水进口温度为21.5～22.5℃,流速为0.104 m·s-1,当温度和流速发生变化时,则重新采取数据。经过计算,确立本模型应提取4个潜变量,由此建立了板式换热器冷却水污垢热阻预测模型。预测结果和实验结果最大相对误差在5.11%以内。结果表明偏最小二乘回归算法的污垢模型预测精度高,所建预测模型是合理可行的。     

Ca~(2+)环境下板式换热器微生物污垢特性

为了研究Ca2+环境下微生物的污垢特性,通过人工配比方法加入Ca Cl2与铁细菌,对板式换热器循环冷却水系统在不同温度、速度和铁细菌浓度下的污垢特性进行了实验研究。结果表明:在Ca2+环境下污垢热阻高于纯铁细菌污垢热阻,且温度越高污垢热阻渐近值越小,流体速度越大污垢热阻渐近值越小,铁细菌浓度越大污垢热阻渐近值越大。     

板式换热器Ni-P-TiO2复合纳米镀层微生物污垢特性

换热器微生物污垢问题普遍存在于能源化工领域,污垢的聚集会导致设备的流动阻力、燃料消耗和维护成本支出大幅度增加。本文采用复合纳米镀层来抑制和减轻换热表面的微生物污垢的附着和沉积。首先采用化学镀的方式,在板式换热器的不锈钢316板上镀覆 Ni-P-TiO₂复合纳米镀层和对照性的Ni-P 镀层。基于板式换热器的微生物污垢在线监测实验系统,研究了镀覆Ni-P-TiO₂复合纳米镀层的板式换热器微生物污垢特性。结果表明,清洁状态下,镀覆两种镀层的板式换热器其摩擦系数（f）和Nusselt数（Nu）相较未镀覆板式换热器均略有增加;微生物污垢实验后,相比较未镀覆的板式换热器,镀覆Ni-P镀层的板式换热器污垢热阻减少了8.36%~23.07%,而镀覆Ni-P-TiO₂复合纳米镀层的板式换热器污垢热阻减少了16.6%~30.96%;在相同微生物污垢实验工况下,镀覆Ni-P-TiO₂复合纳米镀层的板式换热器的摩擦系数（f）相比Ni-P镀层的低2.54%~11.82%,但Nu却明显高于Ni-P镀层达8.47%~9.45%,并且污垢热阻明显小于Ni-P镀层达10.66%~18.18%,镀覆Ni-P-TiO₂复合纳米镀层的板式换热器展现了优异的强化传热性能和抑垢性能。     

2种CaCO_3溶液配制法下板式换热器的污垢特性

为研究板式换热器碳酸钙的污垢特性,以BR0.015F型板式换热器为实验平台,研究了2种配制碳酸钙溶液方法(碳酸钠与氯化钙和碳酸氢钠与氯化钙)在板式换热器下的污垢特性,并用扫描电镜观察结垢表面的晶体类型。结果表明:在相同的实验条件下,碳酸钠法在板片表面结垢薄、易于清除,污垢没有凝结成块状,板式换热器速度场和温度场对污垢分布的影响不明显,扫描电镜观察污垢粉末多为六面体晶型,单个分布未粘结在一起。碳酸氢钠法在板片表面结垢相对致密、难于清除,污垢凝结成块状,板式换热器温度场的分布对污垢分布的影响明显,结垢量的分布与板式换热器数值模拟的温度场分布基本一致,扫描电镜观察污垢发现污垢晶体紧密的粘结在一起。     

水质参数对交叉缩放椭圆管污垢的影响

采用对比的实验方法对交叉缩放椭圆管与光管的污垢热阻进行了分析,并重点研究了冷却水（松花江水）水质参数对污垢产生的影响。实验结果表明：在低流速时,交叉缩放椭圆管的污垢热阻渐近值比光管低,且没有明显的诱导期;实验中冷却水水质参数的变化对污垢影响明显。并深度分析了水质参数随时间的变化及水质参数变化对强化换热表面污垢特性的影响,为换热器提高换热效率提供了参考。     

PTFE管在生活污水中的换热特性研究

研究了浸泡在生活污水中的PTFE管和铝塑管的污垢生长特性和换热性能。根据污垢热阻变化曲线总结出污垢在塑料换热器上生长特性,污垢的生长过程可分为三个阶段:生长阶段,过渡阶段和振荡阶段。通过分析和比较PTFE管和铝塑管的污垢热阻和换热系数,说明了PTFE管在抑制污垢生长和传热性能都优于铝塑管,PTFE材质更适合于污水热能回收系统中。     

换热器因应结垢慢时变的控制系统重构分析

换热器作为化工过程中重要的热量传递设备,一般需要持续运行较长时间,期间由于结垢热阻的不断累积,换热器的换热效率将随时间逐渐下降,直至无法满足工艺要求。在实际的工业换热过程中,工艺人员通常会对换热器进行裕量设计,然而,当换热器需要运行的时间增长或者裕量设计不足时,面对不可避免的结垢增长,常用的流量控制策略在换热器运行末期的调节效果逐渐变差,旁路控制的方案无法实现全周期的持续控制。因此,本文首先在渐近增长模型的基础上建立了换热器结垢累积的积分渐近模型,该模型考虑了过程参数对结垢速率的影响;其次,以一个用于水循环的小面积换热器为例,分析了考虑结垢增长的条件下流量控制和旁路控制的调节效果;最后,针对结垢过程的慢时变和持续性等特点,设计了基于流量与旁路开度的控制系统重构方案。示例的运行结果表明,对于同样面积裕量有限的换热器,这一控制方案能延长其使用寿命,实现其全周期持续可控的目标。     

Roughness and constriction effects on heat transfer in crystallization fouling

This contribution addresses apparent negative fouling resistances for crystallization fouling. Two effects contribute to this phenomenon; surface roughness enhances heat transfer in the roughness controlled phase. In the crystal growth phase, surface roughness as well as the constriction of flow cross section due to the fouling layer build-up is taken into consideration. Fouling experiments were carried out in a double pipe heat exchanger with a supersaturated aqueous CaSO₄ solution at a Reynolds number of 17,500 corresponding to a flow velocity of 0.65 m s⁻¹. The measured pressure drop between inlet and outlet allowed the calculation of the integral friction factor for the current surface roughness. With the given friction factor it was possible to estimate the actual heat transfer coefficient of the inner tube. Accounting for the increase in heat transfer caused by surface roughness in the roughness controlled phase, the fouling resistance was recalculated. In the subsequent growth phase flow acceleration due to constriction effects is considered in addition to the roughness effect. Overall the integral fouling resistance and consequently the deposit thickness are underestimated by a factor of up to 2.5 when simply using heat balance. With the proposed approach apparent negative fouling resistances can be eliminated quantitatively.     

冷却水换热器结垢和腐蚀的原因及处理措施

阐述了冷却水换热器结垢和腐蚀的原因,并对其危害进行了介绍;探讨了结垢和腐蚀的处理措施,为解决冷却水换热器结垢和腐蚀问题提供了借鉴和指导。     

低压静电用于循环冷却水阻垢的实验研究

对低压静电处理循环冷却水的阻垢性能进行了实验研究与机理分析。采用动态监测污垢热阻的方法进行了结垢与阻垢实验,并对溶液的水质进行了分析。结果表明,低压静电处理循环冷却水对换热表面的结垢起到很好的抑制作用,实验中仅需2.2W功率就可达到100%的阻垢率。低压静电水处理不同与其它物理水处理技术,它可降低溶液的硬度、碱度、电导率及pH值,是一种主动的抗垢技术。被处理溶液中发生的微电解反应使更多的污垢晶体在处理器中聚集并生长,而不是沉积在换热表面,从而起到阻垢作用。     

Numerical method for heat transfer and fouling analysis of a shell and tube heat exchanger using statistical analysis

Through proper monitoring, problems can be identified and isolated well before the economics of the process are threatened. In contrast to most conventional methods, fouling can be detected when the heat exchanger operates in transient states. Statistical analysis is used to develop a fouling growth model of a heat exchanger subjected to fouling. The statistical analysis was considered for four different types of distributions out of which the lognormal distribution was found to be most suitable. Experiments were conducted with a single pass shell and tube heat exchanger with water both as the hot and cold fluids. The results show that the proposed tool is very effective in detecting critical fouling in a heat exchanger, which can be utilized for predicting the optimal maintenance schedule. Hence, the results of this work can find application in predicting the reduction in heat transfer efficiency due to fouling in heat exchangers that are in operation and assist the exchanger operators to plan cleaning schedules.     

Impact of deposit aging and surface roughness on thermal fouling: Distributed model

A kinetic model was recently proposed to describe the effect of aging on deposit thermal conductivity and the thermal performance of a shell‐and‐tube heat exchanger undergoing crude oil fouling. The model is adapted for implementation within a dynamic, distributed system with spatial and temporal distributions, relaxing several of the previous assumptions. The evolution of surface roughness is also considered, using conjectural linear and asymptotic functions. Simulations are performed for a single tube representative of a refinery exchanger. The results demonstrate the substantial effects over time of aging and roughness on heat transfer and pressure drop. Roughness effects yield apparently negative initial fouling resistances, as reported in some experimental tests. The importance of accounting for roughness dynamics in short time scale pilot plant scale tests and aging over longer time scales in industrial applications is highlighted. © 2010 American Institute of Chemical Engineers AIChE J, 2010